Coating material for parts of engine exhaust system and method for manufacturing the same

ABSTRACT

Disclosed is a coating material for parts of an engine exhaust system and a method for manufacturing the same. The coating material includes a second junction layer made of CrN or Ti(C)N, a support layer made of TiAlN/CrN disposed on a surface of the second junction layer, and a functional layer made of TiAlN/CrSiN or TiAlN/CrSiCN disposed on a surface of the support layer. The coating material improves abrasion resistance and seizure resistance of the parts of the engine exhaust system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2012-110234, filed on Oct. 4, 2012, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND

(a) Technical Field

The present disclosure relates to a coating material for parts of anengine exhaust system and a method for manufacturing the same, and moreparticularly, to a multi-layered coating material for parts of an engineexhaust system, which includes a first junction layer made of Ti or Cr,a second junction layer made of CrN or Ti(C)N, a support layer made ofTiAlN/CrN, and a functional layer made of TiAlN/CrSi(C)N, all of whichare stacked in sequence. The multi-layered coating of the presentinvention provides improved physical properties, particularly forsliding parts of an engine exhaust system, such as seizure resistance,abrasion resistance and heat resistance.

(b) Background Art

In recent years, as the regulations on automobile exhaust gas have beenreinforced with the rise of environmental issues such as global warming,automakers have made attempts to develop a variety of environmentallyfriendly vehicles so as to reduce the carbon dioxide emissions to 50g/km by 2020, which corresponds to 35 to 50% of the current carbondioxide emissions.

More particularly, to satisfy the corporate average fuel economy (CAFE)standards of reducing the fuel efficiency to 54.5 mpg (23.2 km/l) by2025, active research on technology associated with downsizing or fuelefficiency improvement has been conducted. In particular, an exhaust gasrecirculation (EGR) system has been applied to achieve an increase inengine combustion efficiency and a decrease in generation of NO_(x).

The EGR system is generally composed of a flat valve, a shaft, abushing, a washer, a housing, etc. An actuator is provided outside thehousing for opening/closing the flat valve. In this case, the parts(e.g., the flat valve and the bush, or the washer and the bushing) ofthe engine exhaust system are slid at a high temperature, therebycausing seizure, friction and abrasion of the washer, the flat valve andthe bushing. As a result, the flat valve is not easily opened/closed dueto the seizure, friction and abrasion of the washer, the flat valve andthe bushing. Further, abrasion of the flat valve may cause degradedqualities, such as generation of alarm sounds or noises in the engine.

Therefore, various attempts have been made to prevent shortening of thelifespan of the parts of the engine exhaust system and to maintainperformance of the parts. More particularly, active research on surfacetreatment has been conducted to improve physical properties such asseizure resistance, abrasion resistance, a low friction property, heatresistance, etc.

For example, a CrN coating has been applied in an attempt to maintainperformance of the parts of the engine exhaust system, which issusceptible to abrasion due to the lack of high-temperature hardness.However, even with the CrN coating, hardness of the parts is lowered ata temperature of 500° C. or higher due to the lack of heat resistanceand abrasion of the parts is facilitated due to the low seizureresistance.

In attempts to solve the problems regarding the CrN coating,heat-resistant coating materials such as TiAlN, CrTiSiN or TiAlCrN—CrONhave also been used. However, these heat-resistant coating materialshave difficulties in simultaneously improving the multiple physicalproperties (heat resistance, abrasion resistance, seizure resistance, alow friction property, etc.) of the coating material that are requiredfor sliding parts to operate under a high-temperature environment.

When conventional coating materials, such as a CrN coating material or aTiAlN coating material, are applied to parts of a conventional EGRsystem, a seized product may be easily formed on surfaces of the partsdue to the presence of carbides. In this case, the seized product ismainly responsible for lowering hardness of the parts and shortening thelifespan of the parts, which results from leakage or damage.

The description provided above as a related art of the present inventionis just for helping understanding the background of the presentinvention and should not be construed as being included in the relatedart known by those skilled in the art.

SUMMARY OF THE DISCLOSURE

The present invention provides a coating material for parts of an engineexhaust system and a method for manufacturing the same. The coatingmaterial of the present invention provides excellent physical propertiessuch as heat resistance, high-temperature stability and seizureresistance, as compared to a coating material used for parts of aconventional engine exhaust system, thereby resulting in extendedlifespan of an engine.

According to one aspect, a coating material for parts of an engineexhaust system includes a second junction layer made of CrN or Ti(C)Nand disposed on a surface of a substrate, a support layer made ofTiAlN/CrN and disposed on a surface of the second junction layer, and afunctional layer made of TiAlN/CrSiN or TiAlN/CrSiCN and disposed on asurface of the support layer.

According to various embodiments, the second junction layer has athickness of about 0.1 to about 10 μm, the support layer may have athickness of about 0.5 to about 10 μm, and the functional layer may havea thickness of about 0.5 to about 10 μm.

According to various embodiments, the coating material further includesa first junction layer disposed between the surface of the substrate andthe second junction layer. The first junction layer may be made of Ti orCr.

According to another aspect, the present invention provides a method formanufacturing a coating material for parts of an engine exhaust systemwhich includes: changing an inside of a chamber from a vacuum state to aplasma state, depositing a second junction layer made of CrN or Ti(C)Non a surface of a substrate disposed in the chamber, depositing asupport layer made of TiAlN/CrN on a surface of the second junctionlayer, and depositing a functional layer made of TiAlN/CrSiN orTiAlN/CrSiCN on a surface of the support layer.

According to various embodiments, the second junction layer has athickness of about 0.1 to about 10 μm, the support layer has a thicknessof about 0.5 to about 10 μm, and the functional layer has a thickness ofabout 0.5 to about 10 μm.

According to various embodiments, the depositing of the second junctionlayer is performed by depositing a first junction layer made of Ti or Cron the surface of the substrate, followed by depositing the secondjunction layer.

According to various embodiments, the depositing of the support layermade of TiAlN/CrN is performed by depositing the support layer made ofTiAlN/CrN so that Ti, Al and Cr in the support layer are provided at aratio of about 1:1:1.

According to various embodiments, the depositing of the functional layermade of TiAlN/CrSiN is performed by depositing the functional layer madeof TiAlN/CrSiN so that Ti, Al, Cr and Si in the functional layer areprovided at a ratio of about 1:1:0.9:0.1.

According to various embodiments, the depositing of the functional layermade of TiAlN/CrSiCN is performed by depositing the functional layermade of TiAlN/CrSiCN so that Ti, Al, Cr, Si and C in the functionallayer are provided at a ratio of about 1:1:0.8:0.1:0.1.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of thepresent invention, and wherein:

FIG. 1 is a diagram illustrating a configuration of a TiAlCrSiCN coatingmaterial according to one exemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating a physical vapor deposition (PVD)system configured to prepare a coating material according to oneexemplary embodiment of the present invention;

FIG. 3 is an image taken by testing a conventional coating material,followed by evaluating a seizure property of the conventional coatingmaterial;

FIG. 4 is an image taken by testing the friction abrasion of a coatingmaterial of Comparative Example 1, followed by evaluating a seizureproperty of the coating material;

FIG. 5 is an image taken by testing the friction abrasion of a coatingmaterial of Comparative Example 2, followed by evaluating a seizureproperty of the coating material;

FIG. 6 is an image taken by testing the friction abrasion of a coatingmaterial of Comparative Example 3, followed by evaluating a seizureproperty of the coating material;

FIG. 7 is an image taken by testing the friction abrasion of a coatingmaterial of Example 1, followed by evaluating a seizure property of thecoating material according to one exemplary embodiment of the presentinvention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below.

Prior to the description, it should be understood that the terminologyused in the specification and appended claims should not be construed aslimited to general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentinvention on the basis of the principle that the present inventors areallowed to define the terms appropriately for the best explanation.Therefore, the description proposed herein is just a preferable examplefor the purpose of illustrations only, not intended to limit the scopeof the invention, so it should be understood that other equivalents andmodifications could be made thereto without departing from the scope ofthe invention.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about”.

One aspect of present invention provides a coating material for parts ofan engine exhaust system, which includes a functional layer made ofTiAlCrSi(C)N as a main layer.

According to embodiments of the present invention, parts (e.g., a flatvalve, a shaft, a bush, a washer, etc.) of an engine exhaust system areprovided with high-quality physical properties required to cope withsevere environments to which the parts of the engine exhaust system canbe adapted. in the parts are provided with such properties through theuse of improved coating materials which are capable of improvingmultiple physical properties of the parts, such as heat resistance,abrasion resistance and seizure resistance.

According to aspects of the present invention, a coating material isprovided which is made of TiAlCrSi(C)N.

In the present invention, the term “TiAlCrSi(C)N” refers to TiAlCrSiN orTiAlCrSiCN, the term “TiAlN/CrSi(C)N” refers to TiAlN/CrSiN orTiAlN/CrSiCN, and the term “Ti(C)N” refers to TiN or TiCN.

FIG. 1 is a diagram illustrating a configuration of a TiAlCrSiCN coatingmaterial according to one exemplary embodiment of the present invention;

As shown in FIG. 1, the coating material according to one exemplaryembodiment of the present invention includes a second junction layer 120made of CrN or Ti(C)N and disposed on a surface of a substrate 100, asupport layer 130 made of TiAlN/CrN, and a functional layer 140 made ofTiAlN/CrSi(C)N, all of which are stacked in sequence. Preferably, thecoating material according to one exemplary embodiment of the presentinvention further includes a first junction layer 110 disposed between asurface of the substrate 100 and the second junction layer 120. Thisfirst junction layer 110 is preferably made of Ti or Cr and.

According to embodiments of the invention, when the substrate 100 ismade of a material to be nitrided, a nitriding layer having a thicknessof about 80 to about 120 μm may be formed by the nitriding process.

The first junction layer 110 made of Ti or Cr can be used to improveadhesion between a coating layer and the substrate 100. The secondjunction layer 120 made of CrN or Ti(C)N is can be used to minimize aresidual stress of the coating layer and improve physical propertiessuch as toughness, fatigue resistance and impact resistance.

According to various embodiments, the support layer 130 made ofTiAlN/CrN can be in the formed of a multi-layered nanostructure. Thesupport layer can be used to improve physical properties required forthe parts of an engine exhaust system (such as a flat valve or a bush),such as toughness, heat resistance, anti-oxidation property and abrasionresistance.

According to various embodiments, the functional layer 140 made ofTiAlN/CrSiN or TiAlN/CrSiCN can be in the form of a multi-layerednanostructure. The functional layer 140, can provide the materials witha seizure resistance through the use of silicon (Si), and a low frictionproperty through the use of carbon (C), as well as heat resistance,anti-oxidation property and abrasion resistance.

The thickness of the second junction layer 120 is preferably in a rangeof about 0.1 to about 10 μm. When the thickness of the second junctionlayer 120 is less than about 0.1 μm, the content of the components ofthe second junction layer 120 is not sufficient to show the desiredfunctions. On the other hand, when the thickness of the second junctionlayer 120 exceeds 10 μm, adhesion between the coating material and thesubstrate 100 may be degraded.

In addition, the support layer 130 made of TiAlN/CrN and the functionallayer 140 made of TiAlN/CrSi(C)N, both of which may be provided with amulti-layered nanostructure, may each have a thickness of about 0.5 toabout 10 μm. When the thickness of each of the support layer 130 and thefunctional layer 140 is less than about 0.5 μm, the multi-layerednanostructure may not be easily formed due to mixing of the twodifferent layers, which makes it difficult to provide the desiredeffects of the present invention. On the other hand, when the thicknessof each of the support layer 130 and the functional layer 140 eachexceed about 10 μm, the coherency strain between the two layers may beout of balance, which leads to a decrease in hardness.

In general, it is very difficult to simultaneously improve conflictingphysical properties, for example, abrasion resistance and impactresistance. However, the present invention enables simultaneousimprovement, particularly by using the second junction layer 120 made ofCrN or Ti(C)N, which have excellent impact resistance, as well as thesupport layer 130 made of TiAlN/CrN, which to has excellent abrasionresistance, and the functional layer 140 made of TiAlN/CrSi(C)N.

Another aspect of the present invention provides a method formanufacturing a coating material for parts of an engine exhaust system.The coating material may be prepared using a PVD method, and can includea functional layer made of TiAlCrSi(C)N as a main layer.

Methods of coating a surface of a metal substrate with a coatingmaterial are mainly divided into physical vapor deposition (PVD) methodsand chemical vapor deposition (CVD) methods.

PVD is a dry processing method that provides negative polarity to atarget material (substrate) and deposits an ionized metal material ontoa surface of the target material using electrical attraction whilesupplying the ionized metal material in a steam state. In this case, theionized metal material may be uniformly coated onto the surface of thesubstrate 100, and the adhesion may be enhanced using fine ionparticles.

According to preferred embodiments, the present invention uses an arc,high-power impulse magnetron sputtering (HIPIMS) or inductive-coupledplasma (ICP) method. These methods generate high-density plasma, whichallow for the formation of a nanostructure and high-speed coating ofcoating material particles.

FIG. 2 is a diagram illustrating a PVD system configured to prepare acoating material according to one exemplary embodiment of the presentinvention. As shown in FIG. 2, the PVD system can include a pump 210, aCr target 220, a TiAl target 230, a CrSi target 240, a Ti target 280, agas inlet 250 and a heating unit 260, disposed on a chamber 200, and arotary holder 270 disposed within the chamber 200. Here, the substrate100 is disposed on the rotary holder 270.

Ions required for respective layers constituting the coating materialare supplied to each of the targets, and a desired gas, such as nitrogengas or hydrocarbon gas (in some embodiments, preferably acetylene gas),is introduced into the chamber 200 through the gas inlet 250. In thiscase, nitrogen (N) ions may be supplied as the nitrogen gas, and carbon(C) ions may be supplied as the hydrocarbon gas.

According to various embodiments, a material that can be subjected to anitriding process before the coating process may be coated afterundergoing a nitriding process, followed by removing a compound layer.

According to an exemplary method, first, as pretreatment of the coating,an inside of the chamber 200 is changed into a vacuum state using a pump210 or the like, and is then changed into a plasma state by introducingargon gas or the like through the gas inlet 250.

Next, the chamber 200 is heated to a suitable temperature, such as about80° C., using the heating unit 260 to activate a surface of thesubstrate 100. The surface of the substrate 100 is then cleaned byapplying a bias voltage to allow positive argon ions to collide with thesurface of the substrate 100 (Baking & Cleaning).

Thereafter, nitrogen gas is introduced into the chamber 200 through thegas inlet 250 to form a nitrogen atmosphere in the chamber 200. Then,the second junction layer 120 is deposited on the surface of thesubstrate 100. For example a CrN junction layer 120 may be depositedusing the nitrogen gas and the Cr target 220. Alternatively, a TiNsecond junction layer 120 may be deposited on the surface of thesubstrate 100 using the nitrogen gas and the Ti target 280. Preferably,the second junction layer 120 is deposited to a thickness of about 0.1to about 10 μm. Here, when acetylene gas is introduced with the nitrogengas, the second junction layer 120 made of TiCN may be deposited (PVDmethod).

According to some embodiments, the first junction layer 110 made of Tior Cr is further deposited on the surface of substrate 100 using the Titarget 280 or the Cr target 220 prior to deposition of the secondjunction layer 120 (PVD method). This first junction layer 110 isoptional.

Next, the support layer 130 made of TiAlN/CrN is deposited. According toan exemplary embodiment, the support layer 130 is provided so as to havea multi-layered nanostructure, in which TiAlN layers and CrN layers arealternately stacked on a surface of the second junction layer 120 bypartly exposing the substrate 100, on which the second junction layer120 (and, in some embodiments, the first and second junction layers 110,120) is deposited, to the TiAl target 230 and the Cr target 220 under anitrogen atmosphere using the rotary holder 270. According to apreferred embodiment, the support layer 130 is deposited to a thicknessof about 0.5 to about 10 μm (PVD method).

In this case, the support layer 130 made of TiAlN/CrN is provided so asto improve the toughness, heat resistance, anti-oxidation property andabrasion resistance of the substrate 100. In a preferred embodiment, theTi, Al and Cr in the support layer 130 are deposited at a ratio of 1:1:1based on alternate stacking of the respective layers so as to maximizethe effects of the respective layers.

Thereafter, the functional layer 140 is provided on a surface of thesupport layer. According to an exemplary embodiment, the functionallayer 140 is made of TiAlN/CrSiN, and preferably has a multi-layerednanostructure, in which TiAlN layers and CrSiN layers are alternatelystacked on a surface of the support layer 130. According to a method ofthe present invention, TiAlN layers and CrSiN layers are alternatelystacked on a surface of the support layer 130 by partly exposing thesubstrate 100 on which the support layer 130 is deposited to the TiAltarget 230 and the CrSi target 240 under a nitrogen atmosphere using therotary holder 270. According to an exemplary embodiment, the supportlayer 130 is deposited to a thickness of about 0.5 to about 10 μm. Whenacetylene gas is introduced with the nitrogen gas, the functional layer140 made of TiAlN/CrSiCN may be deposited (PVD method).

In this case, the functional layer 140 made of TiAlN/CrSi(C)N may beprovided to improve seizure resistance and a low friction property aswell as physical properties such as heat resistance, anti-oxidationproperty and abrasion resistance. According to a preferred embodiment,Ti, Al, Cr and Si, or Ti, Al, Cr, Si and C in the functional layer 140are deposited at a ratio of 1:1:0.9:0.1 or 1:1:0.8:0.1:0.1 in analternate stacking arrangement of the respective layers so as tomaximize their desired effects.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Surface CrN TiAlN CrTiSiN TiAlCrSiCN treatment/coatingMethod PVD PVD PVD PVD Coating 30   9.5(5CrN—4.5TiAlN) 10(5CrN—5CrTiSiN)10(4CrN/4TiAlCrN—2TiAlCrCN) thickness (μm) Abrasion (mg) of  7.5 2.3 2.21.48 coating material(disc) Abrasion (mg) of 51.2 29   32   17.1  counterpart material (pin) Friction coefficient   0.63  0.69  0.72 0.42Seizure property Medium Medium Low Low

Table 1 lists the high-temperature friction coefficients, abrasionproperties and seizure properties of the conventional coating materialand the coating material according to an embodiment of the presentinvention for the purpose of comparison. In the case of a conventionalproduct (Inconel 713 C), a coating material had an abrasion of 15.1 mg,a counterpart material had an abrasion of 120.3 mg, and the coatingmaterial and the counterpart material had a friction coefficient of 0.85and a good seizure property.

In this case, the friction coefficient was calculated by measuring afriction coefficient between a coating (disc) and a pin (SUJ2) using apin-on-disc wear tester. The test conditions included a sliding distanceof 2,000 m, a load of 20 N, a rate of 0.1 m/s, and an atmospherictemperature of 700° C., and the seizure property was evaluated after thetest.

As listed in Table 1, it was revealed that the coating material andcounterpart material according to the present invention were measured tohave the lowest abrasions of 1.48 mg and 17.1 mg, respectively, comparedwith the conventional coating material, which results from a lowfriction coefficient. Therefore, it could be seen that the coatingmaterial and counterpart material according to the present invention hadexcellent abrasion resistance and abrasion-attacking property, comparedwith the conventional coating material.

Also, FIG. 3 is an image taken by testing a conventional coatingmaterial, followed by evaluating a seizure property of the conventionalcoating material. FIGS. 4 to 6 are images taken by testing the frictionabrasions of coating materials of Comparative Examples 1 to 3, followedby evaluating seizure properties of the coating materials, respectively.FIG. 7 is an image taken by testing the friction abrasion of a coatingmaterial of Example 1, followed by evaluating a seizure property of thecoating material. From the results obtained by comparing the imagesshown in FIGS. 3 to 7, it could be seen that, unlike the comparativeexamples, a seized product was hardly observed when the coating materialaccording to the present invention was used, which indicates that thecoating material according to the present invention has an effect ofimproving the seizure resistance.

The coating material having the described-above configuration accordingto the present invention improves physical properties such as seizureresistance, heat resistance and abrasion resistance, compared with theparts of the conventional engine exhaust system such as an EGR systembeing coated with a conventional coating material, thereby improvingqualities of the engine parts and maintaining life spans of the engineparts.

Also, the coating material according to the present invention reducesthe friction coefficients of the sliding parts of the engine exhaustsystem to prevent abrasion of the parts caused by the friction under ahigh-temperature condition, thereby preventing a decrease in power of anengine and noise generation from the engine.

Furthermore, the present invention provides a coating technique andcoating that demonstrate excellent physical properties under severeenvironments to cope with an increase in exhaust temperature accordingto Euro 6 and 7 regulations regarding the exhaust gas emission in thefuture.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A coating material for parts of an engine exhaust system, comprising:a second junction layer made of CrN or Ti(C)N; a support layer made ofTiAlN/CrN disposed on a surface of the second junction layer; and afunctional layer made of TiAlN/CrSiN or TiAlN/CrSiCN disposed on asurface of the support layer.
 2. The coating material for parts of anengine exhaust system of claim 1, wherein the second junction layer hasa thickness of about 0.1 to about 10 μm, the support layer has athickness of about 0.5 to about 10 μm, and the functional layer has athickness of about 0.5 to about 10 μm.
 3. The coating material for partsof an engine exhaust system of claim 1, further comprising a firstjunction layer made of Ti or Cr on a surface of which the secondjunction layer is disposed. 4-9. (canceled)